Design of gravity flow underground pipe distribution network in the canal command area

Abstract

The average water use efficiency (WUE) of irrigation projects is assessed to be only of the order of 30-35%. There is a gap between irrigation potential created and utilized, and it is of up-most important to minimize the gap. This can be achieved by use of pipe distribution network (PDN). The objective of this study is to emphasis on the use of underground PDN instead of canal distribution network (CDN) in the command area of irrigation project to improve WUE and to save land taken up by canals. Adoption of buried pipeline distributary systems had lead to the reduction in water conveyance and distribution losses, reduction in the land area taken up by the distribution system and reduction in the maintenance and operating costs of the irrigation system. A cluster of fields (chak) of 12 ha having 640 m length was selected for design of underground PDN alongwith controllable turnout structures. The inlet structure of rectangular shape having 1 m2 area and 2.7 m height was designed just below the canal bank to trap silt. A screen was fixed at the inlet, through which the water enters into underground pipeline by forcing the thrash out of the system. A 20 cm diameter pipe was found suitable for delivering water till the end of PDN which was 560 m away from the inlet, when laid at bed slope of 0.8%. The head loss calculated from Darcy-Weisbach equation was 2.63 m and found to be less than that of available head of 4.77 m. Air vents of 5 cm diameter were also provided at appropriate points to release entrapped air. Eight numbers of outlets were proposed in the design of the underground pipeline system. The outlets deliver water to a diversion box of 45 × 45 × 45 cm. Two outlets of 20 cm diameter were proposed in each diversion box, one for right hand side of fields and other for left side fields for delivering irrigation water directly to the farmer's fields.